Outline. The Goal: a new metric. Objectives. Thermal Metric Project. Westford Symposium C. J. Schumacher Building Science Corporation

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1 Thermal Metric Project Westford Symposium C. J. Schumacher Corporation Outline! Objective! Approach " Apparatus: # Double Guarded Hot Box " Method: # 3 key elements! Some Results! Test Program! Lessons 2 The Goal: a new metric Objectives! Develop a thermal performance rating system or metric that provides a means of crediting properly built assemblies while penalizing poorly built assemblies (of all types) Means of crediting assemblies with good thermal control (materials, system design & construction quality) 3 4 Schumacher 1 of 20

2 What about the old metric? Benefits of R-Value R-Value! Property of a material! Measurement of resistance to heat flow! Proposed in 1945 by Everett Schuman, Penn State s Housing Research Institute 5! Widely Accepted " FTC Regulation! Simple to Measure " Commercially available test machines! Easy to Communicate " ONE Number at standard temperature " Lumps all 3 modes of heat transfer into an effective conductivity # Conduction # Convection # Radiation R-value Survey R-value Survey (pt 2) Assume R30 insulation Does insulation R-value change with outdoor temperature? YES or NO As the outdoor temperature decreases does the R-value: 1. Increase 2. Decrease 3. Both 1 & 2 4. None of the above 5. I don t know, I m still thinking about the BBQ & beer 7 8 Schumacher 2 of 20

3 Some R-Value Measurements! R30 D B A F C 75 F 9 R13 Fiberglass Batt R16 High Density EPS Schumacher 3 of 20

4 R20 XPS (2 months old) R20 XPS (2, 4 months old) R20 XPS (2, 4, 6 months old) R20 XPS (2, 4, 6, 44 months old) Schumacher 4 of 20

5 1 in. Polyisocyanurate Source: NRCA 2010 International Roofing Expo Presentation Cellulose Impact of moisture on measured conductance Limitations of R-Value To develop a new metric! Definition implies thermal performance is constant! Only true if " Effective conductivity is constant " No temperature sensitivity " No airflow sensitivity " No moisture adsorption " Material is homogenous! Characterize in-service thermal performance! Full-scale wood frame wall assemblies! Realistic boundary conditions! Reasonable for some materials! Not reasonable for most real building assemblies under real conditions Schumacher 5 of 20

6 Approach Approach! Research work required the development of new apparatus: " a different type of Hot Box new methods: " unique wall specimens " control of extra boundary conditions " measurement of extra variables Industry Partners! Dow! Greenfiber! Honeywell! Huntsman Polyurethanes! Icynene Insulation System! NAIMA (Certainteed & Johns Manville) Schumacher 6 of 20

7 A Double Guarded Hot Box Apparatus! A Controlled, repeatable conditions! Measure heat & mass flows Schumacher 7 of 20

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9 33 34 Hot Box! Double Guard! Deep Meter Box " accommodate complex geometries " e.g. wall / floor intersections! Meter Box heating & cooling! Measure energy and mass flows " Air transfer system " Tracer gas system Schumacher 9 of 20

10 Hot Box! Wall specimen size: 8 x 12 (2.4 x 3.6 m)! Temperature range: -40 to 150 F (-40 to 65 C)! deltap & air flow: +/-75 Pa & 30 cfm (300 lpm) Method Three Key Elements: Wall specimen blanks! Wall specimen blanks " Wall frames with controlled, realistic & reproducible airflow paths! Testing with imposed pressure difference " 10 Pa driving Exfiltration & Infiltration! Framed walls designed and constructed to allow airflow paths that are " Realistic " Controlled " Reproducible! Measurement of the air movement " Tracer gas for ALL tests Schumacher 10 of 20

11 Airflow path 1 of 3 Airflow path 2 of 3! 1/8 in. horizontal gap between sheathing (per APA installation recommendations)! 3 standard (non-gasketed) electrical boxes and associated wiring (precedence Ober 1994, NAHB 2009) Airflow path 3 of 3 Onysko & Jones! 1/32 in. gaps between top & bottom plates and OSB & GWB! Controlled use high tolerance steel shims! Realistic representative of gaps that open as framing dries & shrinks (Onysko & Jones, 1989)! Reproducible air leakage for the same wall four constructed times: 0.22 to 0.26 cfm50/ft Schumacher 11 of 20

12 Onysko & Jones Shims! At 10 Pa pressure difference shrinkage resulted in 4x increase in air leakage Schumacher 12 of 20

13 49 50 Characterize Air Leakage! Meter Box to Climate Box (Wall Specimen)! Meter Box to Guard Box (Meter Box Seal) Schumacher 13 of 20

14 Realistic boundary conditions Air Pressures Differences Test Segment MB CB ATS Infil Exfil Infil Exfil! 9 Test Segments: " 5 without intentionally induced airflow " 4 with intentionally induced airflow! Weather station wind pressures typically 8-13 Pa! House wind pressures typically 3-5 Pa! But what air pressure difference should be used to induce the airflow? Air Pressure Differences Air Pressure Differences! Stack effect pressures typically 1-2 Pa /floor Tout Stack C F Pa ! Wind pressure: 3-5 Pa! Stack effect: 1-2 Pa! Fan pressures:? but assume negligible! Test air pressure of 10 Pa is reasonable and repeatable *Stack effect pressures for a 2 storey house Schumacher 14 of 20

15 Challenges testing real walls! Realistic wall with airflow paths! Generate realistic temperature conditions! Induce realistic pressure differences! Measure heat & mass! But! airflow can occur in hot boxes even when we don t intentionally induce it Unintended Pressures -1! Air pressure differences exist even when we don t intentionally induce them! Typically between Pa! Can have a significant impact on leaky walls Schumacher 15 of 20

16 Tracer Gas Measurement Tracer Gas Measurement Can impact of air leakage be assessed?! Not easily!! We can t assess the impact of the airflow (i.e. the interaction effect) unless we know how a perfectly airtight wall performs (i.e. when there is no airflow through it)! So! test the wall again with inside and outside sealed Schumacher 16 of 20

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18 Sealed wall test conditions! Again start by characterizing leakage! Test 5 temperature differences Test Segment MB CB ATS! No intentionally induced airflow! Tracer gas measurement of air change Thermal Metric Test Method 1. Construct wall frame 2. Complete construction of wall specimen 3. Test air leaky wall thermal performance a) Characterize leakage (PvsQ) b) 5 climate temps w/ NO* imposed deltap c) 2 climate temps w/ +ve & -ve 10 Pa deltap 4. Seal the wall specimen (inside & out) 5. Test sealed wall thermal performance a) Characterize leakage (PvsQ) b) 5 climate temps w/ NO* imposed deltap 73 Some Test Results 74 Schumacher 18 of 20

19 A proof of concept wall A proof of concept wall! Wall comparison: (Leaky) vs (Tight) " GWB " 2x4 w/ air permeable insulation " 1.5 air impermeable exterior insulation " Vinyl Siding! Wall comparison: (Leaky) vs (Tight) " GWB " 2x4 w/ air permeable insulation " 1.5 air impermeable exterior insulation " Vinyl Siding! NONE of the products produced by the TM industry partners! NONE of the products produced by the TM industry partners A proof of concept wall! Wall comparison: (Leaky) vs (Tight) " GWB " 2x4 w/ air permeable insulation " 1.5 air impermeable exterior insulation " Vinyl Siding Lessons! NONE of the products produced by the TM industry partners 83 Schumacher 19 of 20

20 Lesson 1: Material R-values Lesson 2: Assembly R-value! Temperature effects R-value! Density effects R-value! Moisture content effects R-value! Hand Calculations (parallel path) " Works if # materials have similar R-value (e.g. wood frame wall) " Does not work if # materials have very different R-value # highly conductive layers perpendicular to flow! Computer Simulations (Therm, Heat2, etc.) " Works if there is NO air movement Lesson 3: Hot Box Testing! Airflow impacts common hot box tests!! Tracer gas can be used to measure incidental airflows Description SI Units * British Units Specimen Area m ft 2 Specimen thickness mm in. Average cold side surface temperature C F Average warm side surface temperature C F Temperature differential C F Mean specimen temperature C F Rate of heat flux through the specimen W/m! Btu/h.ft! Thermal conductance of the specimen W/m!.K Btu/h.ft!. F Thermal resistance of the specimen K.m!/W F.ft!.h/Btu Thermal conductivity of the specimen W/m.K Btu.in./h.ft!. F Thermal resistivity of the specimen K.m/W F.ft!.h/Btu.in. Uniform Baffle Air Velocity (Warm Side) 0.22 m/s 0.98 ft/sec Uniform Air Velocity (Cold Side) 3.0 m/s 9.84 ft/sec Pressure Differential Across Specimen Nil Pa Nil psi Warm Side Chamber Relative Humidity 10.1 % RH 10.1 % RH Steady-State Temperature Differential Between Guard & Metering Chamber C F 86 Thank You 88 Schumacher 20 of 20